LOS ANGELES (KABC) -- A former University of Southern California professor accused of engaging in illicit sex acts with children pleaded not guilty to federal charges Thursday afternoon.

The FBI says Walter Lee Williams, 64, allegedly traveled from Los Angeles to the Philippines in January 2011 to engage in sex acts with two 14-year-old boys he met online in 2010.

Williams was arrested in Playa del Carmen, Mexico, on Tuesday after being recognized by a tipster. He returned to Los Angeles Wednesday night....

Williams taught history, anthropology and gender studies at USC until 2011. The investigation into Williams started in 2011 after a student at USC notified authorities that the professor may have targeted young boys for sex....